program sixbytes { www.merlyn.demon.co.uk  >= 2001-11-25 } ;

type A6 = array [1..6] of byte ;
const Q : extended = 1.0/256.0 ;

function TwoTo(const P : integer) : extended ;
var S : extended ; J : integer ;
begin S := 1 ;
  for J := 1 to Abs(P) do S := 2.0*S ; { but see ... }
  if P<0 then S := 1.0/S ;
  TwoTo := S end {TwoTo} ;

function SixToExt(const Six : real{48}) : extended ;
var S : extended ; A : A6 absolute Six ;
begin
  if A[1]=0 then begin SixToExt := 0 ; EXIT end ;
  S := 1.0 + 2.0 *  ((((A[2]*Q+A[3])*Q+A[4])*Q+A[5])*Q+(A[6] and $7F))*Q ;
  if A[6]>127 then S := -S ;
  SixToExt := S * TwoTo(integer(A[1])-129) end {SixToExt} ;

Var J : integer ; Z : real{48} ;

BEGIN ;
Randomize ;
for J := 1 to 10 do begin Z := Random*876 ;
  Writeln(Z:20:12, SixToExt(Z):20:12, SixToExt(-Z):20:12) ;
  end ;
Z := 0 ; Writeln(Z:20:12, SixToExt(Z):20:12) ;
Readln ;
END.  Slightly tested.